1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus including the same, and is suitable for an imaging apparatus using an image sensor, such as a digital still camera, a video camera, a monitoring camera, or a broadcasting camera, or an imaging apparatus, such as a camera using a silver-halide film.
2. Description of the Related Art
In recent years, imaging apparatuses, such as digital still cameras and video cameras using a solid-state image sensor, have become highly functional, and the size of these apparatuses has been reduced. Zoom lenses used in these apparatuses are required to have high magnification and a wide viewing angle, to be small, and to have excellent optical performance in all zoom regions. To respond to such demands, a zoom lens including lens units having positive, negative, and positive refractive power in order from an object side to an image side is known.
However, when high magnification of the zoom lens is achieved, since a focal length at a telephoto end becomes long, the axial chromatic aberration is increased. As a configuration to decrease axial chromatic aberration in zoom lenses with long focal length, Japanese Patent Application Laid-Open No. 2011-53297 discusses a zoom lens using anomalous dispersion glass as a material for a positive lens included in a first lens unit.
Generally, to obtain a small photographic optical system with high magnification, the refractive power of the lens units that configure the photographic optical system may just be increased, and the number of lenses that configure each lens unit may just be decreased. However, when the refractive power of the lens unit is increased, the refractive power of each lens surface of a lens that configures the lens unit is increased, and the thickness of the lens is increased to secure the edge thickness of the lens. As a result, a front lens diameter (front lens effective diameter) becomes large, and it becomes difficult to reduce the overall size of the optical system. Further, the chromatic aberration increases because the focal length at the telephoto end becomes long, and it becomes difficult to correct the chromatic aberration.